Publication Date

2009

Document Type

Thesis

Committee Members

Loren E. Babcock (Committee Member), Christopher Barton (Committee Member), Charles Ciampaglio (Advisor), Charles Ciampaglio (Committee Co-chair), Ernest Hauser (Committee Co-chair)

Degree Name

Master of Science (MS)

Abstract

The most common trilobite in the Silurian carbonates of Ohio - especially the Springfield Dolomite - is a species that has been assigned to at least five genera over the past 100 years. This trilobite has been variously referred to as Calymene celebra, Apocalymene celebra, Flexicalymene celebra, Gravicalymene celebra, and Sthenarocalymene celebra. Reexamination of the species "Calymene" celebra through parsimony and morphometric analysis was conducted to properly place this calymenid species within the correct genus. What compounds the confusion is that the characters used to seperate the genera within the family Calymenidae, and therefore create the basis for the argument to create a new genus, seem weak at best. Coupled with the use of incomplete specimens in the new descriptions, overinflation of genera is not only possible, but a reality.In the past 75 years, the pioneers of trilobite research have labored extensively to classify the family Calymenidae. A major study by Shirley in 1936 attempted to classify the calymenids on the basis of cephalic characteristics - specifically the shape of the glabella, variations in the preglabellar field, and the development of papillate lobes - feeling that other morphological characteristics were conservative at best, and unreliable. Subsequent studies have basically followed Shirley's proposed classifications based upon these objective characters. However, a consistant problem with objective character-based analysis is the subjective nature of description. The purpose of phylogenetic classification (cladistics) is to recognize phylogenetic groups, or taxa, all of whose members are descended from a common ancestor. The common ancestor and all descendents form a monophyletic group. Phylogenetic classification is concerned with grouping individual species into evolutionary categories. Because classification uses both quantitative and qualitative data, the goal was to remove the subjective nature of qualitative data. By using morphometrics to help find similarities within shapes, description of the cephalon can be defined in absolute values instead of subjective descriptions.

Based on quantitative phylogenetic analysis, "Calymene" calymene best fits with Calymene, as originally described by Raymond in 1916. Phylogenetic analysis also indicates that the study genera could be "lumped" into the following generic categories (synonymous genera in parentheses): Alcymene, Calymene (including Calymene celebra), Flexicalymene (including Gravicalymene, Nipponcalymene, Onnicalymene, Metacalymene, and Sthenarocalymene), Diacalymene (including Arcticalymene), Tapinocalymene, and Spathacalymene.

Landmark analysis was used to corroborate the findings of the cladistic analysis. The graphing of Procrutes fitted cephalic landmarks utilizing Principal Component Analysis and Cluster analysis. Landmark analysis indicates that "Calymene" celebra more closely matches with Calymene than the other three study genera to which it has been assigned over the past 100 years. These results directly correlate to the findings in the phylogenetic analysis. As additional specimens are added to the data sets and the groups are rerun, the cluster dendrogram from this group shows "Calymene" celebra to be more similiar to two other species of different genera. As with the previous data set, Alcymene, Arcticalymene, Spathacalymene, and Tapinocalymene are outside the main "nesting" arrangement and can be considered different enough to warrant separate generic assignments. However, the remainder of the specimens are too closely nested to warrant individual generic assignment.

Page Count

108

Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded

2009

Download


Share

COinS